greybus: connection: un-abstract host cport id allocation

I did this recently for the endo id allocation code.

It's clearer now that the allocation of a CPort ID to use for
the AP side of a connection is not very complicated, and it
happens in a pretty controlled environment.  The functions that
abstract getting and releasing those ids don't really add that
much value.

This patch removes gb_connection_hd_cport_id_alloc() and
gb_connection_hd_cport_id_free(), and just open-codes their
activity in the few places they are called.

It is obvious now that the CPort ID allocation isn't done in
atomic context, so we can change the ida_simple_get() call to
use GFP_KERNEL.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>